Nanoscale X-ray imaging of spin dynamics in yttrium iron garnet

Abstract

Time-resolved scanning transmission x-ray microscopy (TR-STXM) has been used for the direct imaging of spin wave dynamics in thin film yttrium iron garnet (YIG) with spatial resolution in the sub 100 nm range. Application of this x-ray transmission technique to single crystalline garnet films was achieved by extracting a lamella (13x5x0.185 µm 3 ) of liquid phase epitaxy grown YIG thin film out of a gadolinium gallium garnet substrate. Spin waves in the sample were measured along the Damon-Eshbach and backward volume directions of propagation at gigahertz frequencies and with wavelengths in a range between 100 nm and 10 µm. The results were compared to theoretical models. Here, the widely used approximate dispersion equation for dipole-exchange spin waves proved to be insufficient for describing the observed Damon-Eshbach type modes. For achieving an accurate description, we made use of the full analytical theory taking mode-hybridization effects into account.

Efficient wavelength conversion of exchange magnons below 100 nm by magnetic coplanar waveguides

“…We argue that the wavelength conversion based on mCPWs is very versatile and works in both insulting and metallic magnets, in nanoscopic ferromagnetic waveguides 45 and skyrmion-hosting materials 46 . The magnons with k max ¼ 62:4 rad μm −1 reported here possess wavelengths shorter than the minimum ones reported so far for nonmagnetic microwave waveguides 14,15,27 and signals are about three orders of magnitude larger (Fig. 6b).…”

“…The lack of efficient transducers is also detrimental in the fundamental sciences when experimentally exploring magnon scattering and band structures in noncollinear spin textures, such as skyrmion lattices 11,12 . Coplanar waveguides (CPWs) with lateral feature sizes down to 125 nm have not yet been sufficient for efficient emission of short-wave magnons [13][14][15] . Instead parametric pumping in the nonlinear regime has been utilized to obtain exchange magnons with k > 20 rad μm −116-18 .…”

Direct observation of coherent magnons with suboptical wavelengths in a single-crystalline ferrimagnetic insulator

“…(1) is not necessarily a valid approximation for the 185 nm film in case of short wavelengths. It has been shown in an earlier experiment [30] that in a YIG film of this thickness hybridization between the fundamental and the first higher order mode in DE geometry can significantly affect the dispersion relation [24,41]. This apparently not being the case here can be explained by the comparatively much higher external magnetic fields applied, which lead to the higher order mode shifting upwards in frequency and no longer crossing the fundamental mode.…”

“…One possible way to achieve a soft x-ray transparent substrate level is cutting out a small, nearly substrate free lamella from the film using focused ion beam (FIB) milling. This approach has been successfully applied recently [30] but it restricts the lateral dimensions of the sample to a few microns and it also limits the means for successive nanofabrication. An approach allowing for more general sample designs is utilizing a combination of mechanical grinding and FIB milling to create local areas of soft x-ray transparency in an extended bulk substrate [31,32].…”

Xenon Plasma Focused Ion Beam Milling for Obtaining Soft X-ray Transparent Samples

“…To overcome the issue of nontransparent substrates, for some material systems selective chemical etching can be applied to specifically remove parts of the sample [9,10]. Another possibility is to extract a lamella out of a thin film or bulk substrate and then place it on a membrane for measurements [11,12]. The disadvantage of this processing is that only a small, confined element and not a full film can be studied.…”